Urethral pressure profile (sphincterometry)

Resting or stress profile of the urethra is used to determine and quantify sphincter insufficiency; however, the method cannot verify subvesical obstruction. Urethral pressure profile measurement is indicated in the assessment of stress incontinence (e.g. post-traumatic, sinus urogenitalis, myelomeningocele). In children, only thin micro-tip catheters with urethral and vesical pressure transducer should be used. A continuous withdrawal is necessary to determine the functional length of the urethra (withdrawal speed of 2-10 cm/min; faster withdrawal produces higher pressure values). At rest, the urethral profile is determined by continuous withdrawal of the measuring sensor. In the urethral stress profile, the pressure in the urethra and the pressure transmission are determined during intermittent intra-abdominal pressure rises (e.g. coughing, Valsalva's manoeuvre). After voiding to completion, the bladder should be filled up to 50% of its maximum capacity with a maximum of 100 mL.

Electromyography (EMG) of the external sphincter

EMG is the study of electrical potentials generated by the depolarization of the external sphincter. For recording, skin surface electrodes are used in children, positioned left and right from the external anal sphincter. EMG should be interpreted in the light of the patient's symptoms, physical findings and urological and urodynamic investigations.

In normal subjects, there is a gradual increase in EMG activity from the pelvic floor during bladder filling; at the onset of micturition, there is complete absence of activity.

The finding of increased EMG activity during voiding, accompanied by simultaneous detrusor pressure and flow changes, is described by the term detrusor-sphincter dyssynergia (in neuropathic bladder/sphincter dysfunction) or detrusor-sphincter dysco-ordination (in neurologically normal children). Because of the many artefacts noted and the inability to distinguish electronic 'noise' from true EMG potentials on the recording, there is no consensus about using the EMG registration.

Table 19: Urodynamics: normal values in children

 

Storage phase
Maximum cystometric bladder capacity:	Age dependent (approx. age x 30)
Residual urine:	< 10 % of the bladder capacity
First desire to void:	Bladder filling > 60 % of the maximum bladder capacity
Intravesical pressure:	14 cmbbO at the beginning, up to 24 стНгО at the end of
	the filling
Involuntary detrusor contraction:	None
Compliance:	> 25 т1_/стНгО
EMG:	Stable
Micturition phase (mictiometry)
Maximum urine flow:	Age dependent
Medium urine flow:	Age dependent
Micturition pressure:	< 75 стЬЮ (age dependent)
EMG:	Fluctuations

EMG = Electromyography

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